Many advanced persistent threat attacks use the malware, believed to have been developed in China

A well-known cyber-spying tool called Gh0st RAT is still being employed in stealthy malware attacks, according to a new report from security firm FireEye.

FireEye, which specializes in malware detection, released data it collected from hundreds of its customers during 2012. It looked at 12 million different reports of suspicious activity, around 2,000 of which were classified as "advanced persistent threats" (APTs), the security industry's term for sophisticated, hard-to-detect attacks aimed at the long-term infiltration of organizations.

Most of those 2,000 incidents employed Gh0st RAT, a remote access tool believed to have been developed in China that allows attackers to steal information from a victim's computers. In 2009, researchers with the Information Warfare Monitor, a computer security research project, and the University of Toronto reported an extensive cyber espionage campaign using Gh0st RAT that targeting more than 1,000 computers in 103 countries.

Gh0st RAT is "a real important part of many types of APT campaigns because it is an effective tool," said Rob Rachwald, FireEye's senior director of market research.

FireEye's report broadly looks at how attackers extract information from victims and control their malware on infected computers, or "callback" activity. Their data from 2012 shows that attackers are using command-and-control servers to deliver instructions to malware in 184 countries now, a 42 percent increase over 2010.

South Korea has a concentration of callback activity. The servers of technology companies tend to be targeted by hackers to communicate with their infected machines. "I think the fact that they've been traditionally one of the most connected nations in the world is probably another driver for this," Rachwald said.

FireEye's report said "in a sense, South Korea is plagued by RATs [remote access tools]. It is clear from the 2012 data that South Korea is one of the top callback destinations in the world and that some of the country's callback activities are associated with more targeted attacks."

Hackers were also inserting stolen information into JPEG image files in order to make the data look more like normal traffic. The malware also used social networking sites such as Twitter and Facebook to place instructions for infected machines, FireEye said.

The company noticed other changes in hackers' behavior. Usually, command-and-control servers were located in a different country than the victim. Now they are locating the command infrastructure in the same country in order to make the traffic look normal.

But for some countries, hackers didn't bother with control servers in a target's country. Canada and the U.K. both had high percentages of callback traffic going overseas. Attackers perhaps didn't do that in those countries because "they knew they weren't going to get detected," Rachwald said.